The use of silica solutions and silica gels to solidify soil and render soil impermeable are well known in the art. U.S. Pat. No. 3,552,130 entitled, “Method of Forming a Substantially Liquid Impervious Wall in an Earth Formation”, and which is incorporated herein by reference, discloses introducing materials into a soil in which a filler material is mixed with a silica gel to form a material which will render certain soil types impermeable.
U.S. Pat. No. 3,375,872, entitled “Method of Plugging or Sealing Formations With Acidic Silicic Acid Solutions”, and which is incorporated herein by reference, discloses a method of sealing earth formations using a low pH silicic acid solution.
It is also known in the art to introduce oils such as a vegetable or mineral oil into a below ground contaminated area. The oil serves to concentrate and remove organic contaminants from the soil so that the contaminants may be removed by recovery of the oil or may be metabolized by microorganisms which may be introduced into the oil fraction. One such use of this technology is seen in U.S. Pat. No. 5,265,674 entitled “Enhancement of in Situ Microbial Remediation of Aquifers”, and which is incorporated herein by reference.
One difficulty of contamination remediation in the vadose zone is the tendency for treatment materials to flow straight down with little lateral spreading. In addition, low viscosity materials leave low concentrations of the treatment materials in the soil pore spaces. Higher viscosity materials increase the saturation of the materials within the soil pore spaces but are difficult to emplace within a significant sized volume needed for typical remediation environments.
Other difficulties of contamination remediation in the vadose zone is that the vadose zone tends to be highly gas permeable, has a moisture content that is less than saturation, and a pressure that varies due to atmospheric pressure variations which create significant gas fluxes. The vadose zone can be highly permeable to the influx of rain and surface water which can leach contaminants into the groundwater. Oxygen and other gases enter the vadose zone through the percolation of rain and surface water and through gas exchange by diffusion and from barometric pressure differentials with the surface. As a result of these properties, it is difficult to perform certain bioremediation and physical techniques within the vadose zone given the permeability, and the open, porous nature of the vadose region.
An additional difficulty of contamination remediation involves adequate treatment of the capillary fringe area associated with a vadose zone. The capillary fringe is a boundary region separating the water table from the unsaturated vadose zone and traditional remediation techniques such as soil vapor extraction or pump and treat protocols are not effective for treatment of a capillary fringe region. The capillary zone may include tension-saturated soils which, depending upon the pore size of the soil, may extend several feet above the water table. Efforts to effectively remediate within the capillary zone have proven difficult given that significant fluctuations of the water table repositions the capillary fringe, thereby subjecting the capillary fringe region to a range of varying conditions of moisture, oxygen availability, and bioavailability of resources.
An additional difficulty of contamination remediation involves adequate treatment of contaminants in the saturated zone. Low permeability zones in the saturated zone can retain contaminants for long periods of time and can slowly release them (back diffusion) over decades leading to a long period of active remediation. Efforts to effectively reduce the contaminant flux from these zones have not been addressed.
An additional difficulty of contaminant remediation concerns dense non-aqueous phase liquid (DNAPL) pools in the saturated zone. These pools reside on top of low permeability soils in more permeable soils where the groundwater flows. The DNAPL pools are sparingly soluble and provide a constant source of contamination to the groundwater and are difficult to treat.
Accordingly, there remains room for improvement and variation within the art.